Right click is not possible on touchscreens, so our right click menu would be inaccessible.
Here we use GtkGestureLongPress to create our right click menu, but only on touch devices.
There's one quirk, and it's that we aren't picking up selected text with the gesture. This is similar to how other mobile clients do it, allowing you to only copy all the text rather than a selection. Would we want to keep that behavior here?